Field of Technology
The present invention concerns a surgical drill-guide. In particular, the present invention relates to a surgical guide for drilling an irregular-shaped body.
Related Art
The shoulder is a ball and socket joint made up of the clavicle, the scapula and the humerus, and associated muscles, ligaments and tendons. It is formed by the articulation between the medial anterior surface of the head of the humerus and the glenoid fossa of the scapula. The shallowness of the fossa and relatively loose connections between the shoulder and the rest of the body provides the arm with a huge range of motion, and make it an extremely mobile joint. The shoulder can abduct, adduct, rotate, be raised in front of and behind the torso, and move through a complete cycle in the sagittal plane.
However, this tremendous mobility makes the shoulder quite unstable and far more prone to dislocation and injury than most other joints in the body.
The shoulder joint is stabilised by the shoulder capsule and a ring of cartilage surrounding the glenoid, which is known as the shoulder labrum. The capsule is formed by a series of ligaments which connect the humerus to the glenoid. When the labrum and/or ligaments have torn or where the ligaments have been hyper-extended, the shoulder becomes unstable and will naturally have a greater tendency to dislocate. This instability can lead to further shoulder problems and, in particular, dislocation and subluxation—where the joint is hyper-mobile but does not dislocate. As a result of shoulder instability it is more likely that repeated dislocations or subluxations will occur during active movement or exercise.
Instability of the shoulder can be caused by a traumatic dislocation, atraumatic dislocation or a non-traumatic dislocation.
Traumatic dislocation occurs when the shoulder is subjected to an adverse force which is sufficient to pull the shoulder out of joint. This can occur through a sporting injury or a traumatic accident such as experienced in a road traffic accident. Due to the large forces associated with such an injury, the labrum can be torn from the bone, creating a Bankart lesion, and this can result in an unstable shoulder. Such an injury can lead to subsequent episodes of dislocation.
An atraumatic dislocation occurs when the shoulder is dislocated through only a nominal force, such as when reaching upwards or when turning in bed. In most cases, the shoulder will relocate itself with a little help. This type of dislocation is relatively common in people with hyper-flexible joints and is associated with certain orientations in the arms of sufferers. This over-flexibility of the joint is generally associated with the way in which the muscles around the shoulder interact with each other, which can produce an imbalance in the control of the joint. In some cases, these problems can be overcome with physiotherapy.
In addition, in a limited number of people their shoulders can undergo positional non-traumatic dislocation. The shoulders of sufferers of this condition are so loose that they can simply ‘fall’ out of joint. This type of dislocation is usually painless and can be relocated easily. Typically, both shoulders are involved and dislocation usually occurs as a result of abnormal muscle function in which the shoulder is pulled out of joint when it is moved in a particular direction. Dislocation can occur with innocuous movements such as when lifting the arm above the head and to the side or forwards. Again, physiotherapy can help to correct this problem by synchronising the muscles to work correctly.
Occasionally, in instances of repeated dislocation and/or subluxation, the problem can generally only be remedied through surgery.
In surgery to correct shoulder abnormalities or injury it is sometimes necessary to drill into or through an irregular-shaped body. For example, in a Latarjet shoulder procedure approximately 15 mm of the tip of the coracoid process is transferred, along with the conjoined tendon, to the glenoid rim. This forms an extension of the glenoid surface and produces a restraint to the shoulder which helps to prevent further dislocation.
During the Latarjet procedure the coracoid process is divided at its base with the coraco-acromial ligament and the conjoined tendon. The pectoralis minor muscle is released from the coracoid process, the subscapularis muscle is split and the capsule of the shoulder joint opened to expose the front of the glenoid. After the glenoid has been prepared, the coracoid is attached and the coraco-acromial ligament is used to strengthen the joint capsule.
In movements involving the arm being lifted above the head (abduction and rotation), the muscles which are relocated over the subscapularis act to prevent dislocation of the shoulder joint.
A critical element of this procedure is the drilling of a hole along the central axis of the coracoid process. This allows a screw to be driven down the centre of the coracoid and into the glenoid to secure the graft thereto (FIG. 1). During this process it is crucial that the position of the graft is held securely and that the graft does not split.
During the procedure the surgeon is able to view the tip of the coracoid, and hence the starting point of the drill, but the position of the drill once it enters the tip is determined purely through guesswork by the surgeon estimating its direction of travel. This is especially true when the procedure is performed arthroscopically as the surgeon's view of the anatomy at the surgical site is by means of a monitor, and rendered in two dimensions. This is not ideal and can lead to fractures in the graft and subsequent problems with its attachment to the glenoid.
The present invention seeks to overcome the above issues by providing a drill-guide for use with an irregular-shaped body.